Sinocalliopteryx (meaning 'Chinese beautiful feather') is a genus of compsognathid dinosaur from the Lower Cretaceous Yixian Formation of China. While similar to the related Huaxiagnathus, Sinocalliopteryx is larger, and at 2.37 meters (7.78 ft) in length, it is the largest known compsognathid genus, and the large size of this "giant compsognathid" lent Sinocalliopteryx its specific name, S. gigas, meaning 'giant.' Sinocalliopteryx is also distinguished from Huaxiagnathus, as well as other compsognathids, by its relatively long hands in relation to its arms, which were also longer overall than in most compsognathids, a feature possibly related to its size.
The well-preserved skeleton of Sinocalliopteryx contained the partial leg of a dromaeosaurid within the abdominal cavity, comprised of a complete lower leg and foot with toes and claws in their natural, articulated position. While the leg is very large in relation to the abdominal cavity, it is clearly situated within it, lying between the ribs. Ji and colleagues, who described Sinocalliopteryx in 2007, suggested that this could indicate it preyed upon the smaller, bird-like dinosaur. This discovery indicated that Sinocalliopteryx may have been an agile, active, "fierce" predator, especially since other compsognathids have been found with (presumably fast-moving) lizards and small mammals in their abdominal cavities.
In addition to the dromaeosaurid leg, four irregularly-shaped stones were found in the abdomen, with no similar stones present in any other portions of the skeleton or embedded in the surrounding rock. The authors interpreted these as gastroliths (gizzard stones) similar to those found with Nqwebasaurus and Baryonyx. Other theropods, such as Caudipteryx and a Mongolian ornithomimid, were also found with gastoliths, though in those cases the stones were much more numerous and smaller in size. Ji and colleagues speculated that, since the later two dinosaurs were probably primarily herbivores, the number and size of gastroliths may correspond with diet; that is, herbivores ingested many small stones, while carnivores ingested only a few larger stones to aid in digestion.
The large size of Sinocalliopteryx compared to its relatives is also notable, and may indicate a trend towards large size among compsognathids (a group well-known for their small size compared to other, giant theropod dinosaurs), similar to the trends towards larger sizes in other dinosaurian lineages.